U.S. patent number 10,741,353 [Application Number 16/362,837] was granted by the patent office on 2020-08-11 for electron emitting construct configured with ion bombardment resistant.
This patent grant is currently assigned to NANO-X IMAGING LTD. The grantee listed for this patent is NANO-X IMAGING LTD. Invention is credited to Koichi Iida, Hidenori Kenmotsu, Hitoshi Masuya.
![](/patent/grant/10741353/US10741353-20200811-D00000.png)
![](/patent/grant/10741353/US10741353-20200811-D00001.png)
![](/patent/grant/10741353/US10741353-20200811-D00002.png)
![](/patent/grant/10741353/US10741353-20200811-D00003.png)
![](/patent/grant/10741353/US10741353-20200811-D00004.png)
![](/patent/grant/10741353/US10741353-20200811-D00005.png)
![](/patent/grant/10741353/US10741353-20200811-D00006.png)
![](/patent/grant/10741353/US10741353-20200811-D00007.png)
![](/patent/grant/10741353/US10741353-20200811-D00008.png)
![](/patent/grant/10741353/US10741353-20200811-D00009.png)
![](/patent/grant/10741353/US10741353-20200811-D00010.png)
View All Diagrams
United States Patent |
10,741,353 |
Kenmotsu , et al. |
August 11, 2020 |
Electron emitting construct configured with ion bombardment
resistant
Abstract
A robust cold cathode uses an electron emitting construct design
possibly for an x-ray emitter device. The electron beam emitted by
the emitting construct is focused and accelerated by an electrical
field towards an electron anode target. A shield is provided to
prevent a cold cathode from being damaged by ion bombardment in
high-voltage applications and a non-emitter zone may provide a
robust ion bombardment zone. The system is further configured to
provide an angled target anode or a stepped target anode to further
reduce the ion bombardment damage.
Inventors: |
Kenmotsu; Hidenori (Machida,
JP), Masuya; Hitoshi (Kashiwa, JP), Iida;
Koichi (Kayabe, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NANO-X IMAGING LTD |
Neve-Ilan |
N/A |
IL |
|
|
Assignee: |
NANO-X IMAGING LTD (Neve-Ilan,
IL)
|
Family
ID: |
53198439 |
Appl.
No.: |
16/362,837 |
Filed: |
March 25, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190221398 A1 |
Jul 18, 2019 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
15038737 |
|
10269527 |
|
|
|
PCT/IB2014/066361 |
Nov 26, 2014 |
|
|
|
|
62013567 |
Jun 18, 2014 |
|
|
|
|
61909387 |
Nov 27, 2013 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J
35/112 (20190501); H01J 35/065 (20130101); H01J
35/14 (20130101); H01J 2235/062 (20130101); H01J
2235/086 (20130101); H01J 1/3042 (20130101) |
Current International
Class: |
H01J
35/06 (20060101); H01J 35/08 (20060101); H01J
35/14 (20060101); H01J 1/304 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kao; Chih-Cheng
Attorney, Agent or Firm: AlphaPatent Associates, Ltd.
Swirsky; Daniel J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser.
No. 15/038,737, filed May 24, 2016, which is a National Phase
Patent Application under 35 U.S.C. 371 of International Patent
Application No. PCT/IB2014/066361, which has an international
filing date of Nov. 26, 2014, and which claims priority and benefit
from U.S. Provisional Patent Application No. 61/909,387, filed Nov.
27, 2013, and U.S. Provisional Patent Application No. 62/013,567,
filed Jun. 18, 2014, the contents and disclosure of which are
incorporated herein by reference in their entirety.
Claims
What is claimed is:
1. An x-ray emitting device comprising: an electron anode target;
and a cold cathode electron source having at least one electron
emitting zone configured to emit electrons towards said electron
anode target, and at least one non-emitting ion bombardment zone,
wherein said at least one electron emitting zone further comprises
an electrically insulating substrate, an array of nano-Spindt field
emission type electron sources, a plurality of control contacts
configured for controlling said electron sources, a focus electrode
configured for applying a voltage above said array, and a shield
disposed over said control contacts, said shield constituting part
of the focus electrode, and wherein said at least one non-emitting
ion bombardment zone is disposed along a line perpendicular to the
surface of said electron anode target; said at least one ion
bombardment zone being distinct from said electron emitting zone of
said cold cathode electron source.
2. The x-ray emitter device of claim 1, further comprising a focus
structure configured to direct electron towards said electron anode
target such that said electrons strike an electron focal spot at an
angle.
3. The x-ray emitter device of claim 2, wherein said at least one
ion bombardment zone is disposed along a line perpendicular to the
surface of said electron anode target at said electron focal
spot.
4. The x-ray emitter device of claim 2, wherein said at least one
ion bombardment zone has larger dimensions than said electron focal
spot.
5. The x-ray emitter device of claim 2, wherein said at least one
ion bombardment zone is coated with an elemental material.
6. The x-ray emitter device of claim 5, wherein said elemental
material comprises a pure metal.
7. The x-ray emitter device of claim 5, wherein said elemental
material comprises carbon.
8. The x-ray emitter device of claim 2, wherein said at least one
ion bombardment zone comprises a central region surrounded by said
electron emitting zone of said cold cathode electron source.
9. The x-ray emitter device of claim 2, wherein the electrically
insulating substrate is silicon-based.
Description
FIELD OF THE INVENTION
The present disclosure is directed to providing a field emitter for
an x-ray source and an electron emitting construct for a device,
such as an image capture device or an x-ray emitter, comprising
field emission type electron sources. In particular, the electron
emitting construct is configured to facilitate radiation in the
X-ray spectrum and further relates to a system and method for
preventing a cold cathode from being damaged by ion bombardment in
high-voltage applications.
BACKGROUND OF THE INVENTION
Typically, an imaging device using a photoelectric layer in
combination with an array of field emission type electron sources
employs passive matrix activation or active matrix activation. In
certain known active matrix activation methods, a particular
electron source is activated through the use of two lines, a column
selection line (e.g., from a column scanning driver) and a row
selection line (e.g. from a row scanning driver), where of one of
signal lines also serves as the voltage source to provide power to
the selected electron source. In the case of field emission type
electron source arrays employing such an activation system, the
selection/voltage source line requires the capability of handling a
voltage of tens of volts. When such high voltages are used in a
signal selection circuit, the consumption of electric power due to
the switching activity becomes extremely high, because the level of
electric consumption is a function of a square of the voltage.
Further, when the voltage in the signal line is large, the ability
of the switching circuit to operate under a fast response time is
adversely affected due to distortion of the voltage waveform.
In certain hold-type display devices using active matrix
activation, the voltage source is separate from the two selection
lines (column and row). That is, a particular electron source is
activated through the activation of a first signal line and a
second signal line, in addition to the voltage for activating the
electron source being provided through a third voltage supply line.
Typically, one of the two signal lines provides signals of varying
voltages to control the length of electron source activation and
thus the level of total electron emission (e.g., to control the
pixel display intensity). Consequently, the voltage of the signal
line carrying the pixel intensity signal may be large, e.g., 15
volts, which results in high energy consumption and a degradation
of the response time capability of the switching circuit. Further,
the switching time of the activation transistor is limited by the
charging time and the charging capacity of the associated
capacitor. For these reasons, such systems are not well suited for
high speed operations such as dot by dot (or line by line)
sequential activation.
Further, X-rays are a form of electromagnetic radiation, which are
typically generated by an x-ray generator. An x-ray generator is a
device used to generate x-rays, typically used in radiography to
acquire an x-ray image representing the inside of an object
enabling imaging of the human body for diagnosis or treating
medical problems, for example. X-ray technology may further be
used, apart from medicine, in fields such as non-destructive
testing, sterilization, florescence and the like.
X-ray tubes, typically comprise a cathode assembly configured to
emit electrons into the vacuum and an anode assembly configured to
collect the electrons and the tube housing, thus establishing a
flow of electrical current, known as the electron beam, through the
tube. A high voltage power source is connected across the cathode
and the anode to accelerate the electrons, striking the target at
high speed after being accelerated. The electron beam is focused
and strikes the anode target at a focal spot. Thus, electrons from
the cathode collide with the anode material, such as tungsten,
molybdenum or copper, and accelerate other electrons, ions and
nuclei within the anode material. About 1% of the energy generated
is emitted/radiated, usually perpendicular to the path of the
electron beam, as x-rays. The rest of the energy is released as
heat.
It is particularly noted that a typical x-ray source has a filament
type hot cathode for its emitter, which is heated by an electric
current passing through the filament. Another type of cathode that
is not electrically heated by a filament is a cold cathode, which
may be used as a replacement for the hot cathode. However cold
cathode x-ray sources lack robustness in high voltage
applications.
In high voltage applications using an emitter such as an x-ray
source, some of the (de)gas molecules from the anode are ionized
and accelerated in a beam of ions towards the emitting cathode.
This beam can cause severe damage to the emitters due to the high
energy ion bombardment.
There is a need for a robust cold cathode resilient to such ion
bombardments in high voltage applications. The current disclosure
addresses this need.
SUMMARY OF THE INVENTION
According to one aspect of the presently disclosed subject matter,
there is provided an electron emitting construct comprising: an
array of field emission type electron sources and a plurality of
control contacts configured for controlling the electron sources; a
focus electrode configured for applying a voltage above the array;
and a shield disposed over the control contacts.
The shield may constitute part of the focus electrode.
The electron sources may be nano-Spindt emitters.
The electron emitting construct may further comprise an
electrically insulating substrate. The substrate may be made of a
ceramic material.
The electron emitting construct may further comprise an emitter
chip mounted to a top-facing chip-mounting surface of the
substrate, the array and control contacts being disposed on a top
side of the emitter chip.
The substrate may comprise control vias corresponding to each of
the control contacts, wherein a top end of each via is disposed
below the shield.
The emitter chip may comprise a plurality of vias configured to
facilitate bringing each of the control contacts into electrical
communication with its corresponding control via.
The electron emitting construct may further comprise a plurality of
external conductors, connecting between each of the control
contacts and its corresponding control via.
The substrate may comprise one or more vias configured to
facilitate bringing a bottom surface the emitter chip into
electrical communication with a bottom surface of the
substrate.
The substrate may be configured to bring the focus electrode into
electrical communication with a bottom surface of the
substrate.
According to another aspect of the presently disclosed subject
matter, there is provided an image capture device comprising an
electron emitting construct as described above.
According to another aspect of the presently disclosed subject
matter, there is provided an x-ray emitting device comprising an
electron emitting construct as described above.
According to another aspect of the presently disclosed subject
matter, there is provided an x-ray emitter device, comprising: an
electron anode target, producing an electric field adjacent to its
surface; and a cold cathode electron source having at least one
electron emitting zone configured to emit electrons towards said
electron anode target;
The x-ray emitter device further comprises: at least one ion
bombardment zone disposed along a line perpendicular to the
electric field adjacent to the surface of the electron anode
target; the at least one ion bombardment zone being distinct from
the electron emitting zone of the cold cathode electron source.
The x-ray emitter device further comprising a focus structure
configured to direct the electrons towards the electron anode
target such that the electrons strike an electron focal spot at an
angle.
As appropriate, the at least one ion bombardment zone of the x-ray
emitter device is disposed along a line perpendicular to the
surface of the electron anode target at the electron focal
spot.
As appropriate, the at least one ion bombardment zone of the x-ray
emitter device has larger dimensions than the electron focal
spot.
The at least one ion bombardment zone of the x-ray emitter device
may be coated with an elemental material. The elemental material
may be selected from a group including a pure metal and carbon.
The at least one ion bombardment zone of the x-ray emitter device
may comprise a central region surrounded by the electron emitting
zone of the cold cathode electron source.
The non-emitter zone of the x-ray emitter device is set between
constructs of the emitting zones of the cold cathode electron
source.
The electrically insulating emitter substrate of the x-ray emitter
device further comprising an emitter chip mounted to a top-facing
chip-mounting surface of the electrically insulating emitter
substrate.
The electron anode target of the x-ray emitter device may comprise
an angled electron anode target configured to form an angle to the
electron emitting source. Where appropriate, the electron angled
anode may further comprise a step to form a stepped electron
anode.
The focus structure of the x-ray emitter may be operable to direct
the electrons to a focal spot close to the step.
The angle of the angled electron anode target of the x-ray emitter
device may be selected such that the ion bombardment zone is
outside an emitter area of the cold cathode electron source.
The electron emitting zone of the x-ray emitter device may comprise
a plurality of field emission type electron sources.
The field emission type electron source of the x-ray emitter device
may be a Spindt-type electron source.
The x-ray emitter device further comprising a resistive layer
situated between the field emission type electron source and the
cathode.
The substrate of the x-ray emitter device may be silicon-based or
silicon carbide-based.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention and to show how it may
be carried in practice, reference will now be made, purely by way
of a non-limiting example, to the accompanying drawings.
With specific reference now to the drawings in detail, it is
stressed that the particulars shown are by way of example and for
purposes of illustrative discussion of the preferred embodiments of
the present invention only, and are presented in the cause of
providing what is believed to be the most useful and readily
understood description of the principles and conceptual aspects of
the invention. In this regard, no attempt is made to show
structural details of the invention in more detail than is
necessary for a fundamental understanding of the invention; the
description taken with the drawings making apparent to those
skilled in the art how the several forms of the invention may be
embodied in practice. In the accompanying drawings:
FIG. 1 is a schematic drawing of a device according to the
presently disclosed subject matter;
FIGS. 2A and 2B are side sectional views of examples of electron
emitting constructs of the image capture device illustrated in FIG.
1;
FIG. 3 is a top view of an emitter chip of the electron emitting
constructs illustrated in FIGS. 2A and 2B;
FIG. 4A is a plan view of a portion of a chip-mounting surface of a
substrate of the electron emitting constructs illustrated in FIGS.
2A and 2B;
FIG. 4B is a plan view of a portion of a bottom surface of the
substrate;
FIG. 5A is a schematic drawing of an example of a reflection-type
device according to the presently disclosed subject matter;
FIG. 5B is a schematic drawing of an example of a transmission-type
device according to the presently disclosed subject matter;
FIG. 6A is a schematic drawing of an embodiment of bombardment
resistant cold cathode x-ray emitter apparatus;
FIG. 6B is a schematic representation of ion pressure distribution
between the electron emitting cathode and the anode target of the
x-ray emitter apparatus, when an electron beam is accelerated
toward the anode target and metal vapor released from the target is
partially ionized;
FIG. 7 represents a top view and cross section of a first
embodiment of an electron emitting cathode of an x-ray emitter
having a non-emitting ion collection zone surrounded by an emitting
zone;
FIG. 8A is a top view plan of a square emitter configuration having
a square non-emitting ion collection zone surrounded by the
emitting zone;
FIG. 8B is a top view plan of a rectangular emitter configuration
having a rectangular non-emitting ion collection zone arranged
between two emitting zones;
FIG. 8C is a top view plan of a circular emitter configuration
having a circular non-emitting ion collection zone surrounded by a
circular emitting zone;
FIG. 9 illustrates a second embodiment of a bombardment resistant
cold cathode x-ray emitter apparatus including an angled target
anode;
FIG. 10A is an illustration of an angled anode;
FIG. 10B is an illustration of a stepped anode;
FIG. 11 is an illustration of a beam landing simulation
configuration;
FIG. 12A is a represents a possible emitter chip of the system;
FIG. 12B is a graph presenting the results of a simulation showing
ion landing simulation on a different anode-cathode distance using
1 mm diameter of electron beam focal spot size;
FIGS. 13A and 13B illustrate selected electron beam simulation for
different anode surface angles;
FIG. 14A is a schematic presentation of beam landing simulation
results for various electron anode angles;
FIG. 14B is a graph presenting the results of a beam landing
simulation on various anode-cathode distances using a 1 mm diameter
of electron beam focal spot size;
FIGS. 15A and 15B illustrate ion trajectory differences between an
angled anode and a stepped anode;
FIGS. 16A and 16B illustrate ion landing spot differences between
an angled electron anode and a stepped electron anode; and
FIG. 17 is a graph presenting the results of a simulation showing
the shift of the ion landing spot using an angled anode, with and
without a step.
DETAILED DESCRIPTION
Electron Emitting Construct:
As illustrated schematically in FIG. 1, there is provided a device,
which is generally indicated as 10. The device 10 comprises an
electron emitting construct 12, constituting a cold cathode of the
emitter, and an electron receiving construct 14, constituting an
anode of the emitter. Electron emitting construct 12 is configured
for emitting an electron beam toward the electron receiving
construct 14, which then produces radiation in a predetermined
spectrum, as is described below. The device may be, for example, an
x-ray emitter, an image capture device, etc.
As illustrated in FIGS. 2A and 2B, the electron emitting construct
12 comprises an emitter chip 18 to which an array 20 of field
emission type electron sources 22 is mounted. A focus electrode 24,
comprising an overhang 26 partially disposed over the emitter chip
18 and being formed with an opening 28, is disposed above the
electron emitting construct 12. In particular, the overhang 26 is
disposed over a margin area 30 of the emitter chip 18, while the
opening 28 is disposed over the array 20 of field emission type
electron sources 22. The electron emitting construct 12 and the
focus electrode 24 are mounted on an electrically insulated
substrate 32.
The electron sources 22 may be any element suitable for selectively
generating electron beam, for example by quantum mechanical
tunneling. Non-limiting examples of suitable electron sources 22
include nano-Spindt emitters, carbon nanotube type electron
sources, metal-insulator-metal type electron sources,
metal-insulator-semiconductor type electron sources. Alternatively,
the array may comprise a combination of different types of electron
sources 22.
The substrate 32 may be made of any suitable material which
provides electrical insulation. For example, it may be made of
ceramic.
In order to power the emitter chip 18, the substrate 32 is provided
with one or more chip vias 34, which bring a top-facing
chip-mounting surface 36 of the substrate 32 into electrical
communication with a bottom surface 38 thereof. (In the present
disclosure, the terms "upper", "top", "lower", "bottom", and
similar terms are used with reference to the orientation
illustrated in the reference to figure.) An electrically conductive
contact plate 40 is provided at the bottom surface 38. Thus, a
power source may be used to provide the necessary electrical power
to the emitter chip 18 by utilizing the contact plate 40 and chip
vias 34 to connect to the emitter chip.
As illustrated schematically in FIG. 3, the emitter chip 18
comprises a plurality of row control contacts 42 along one side
thereof, and column control contacts 44 along with an adjacent side
thereof. The control contacts 42, 44 are disposed within the margin
area 30 of the emitter chip 18, and are thus shielded by the
overhang 26 of the focus electrode 24. They define a grid on which
the field emission type electron sources 22 are arranged. Each of
the electron sources 22 are controlled by activating both its
respective row control contact 42 and column control contact 44.
For example, the electron source 22 indicated at 22a may be
controlled by activating the row control contact indicated at 42a
and the column control contact indicated at 44a.
As illustrated in FIG. 4A, the chip-mounting surface 36 of the
substrate 32 is provided with a plurality of row control pads 46,
e.g., arranged in a line, corresponding to the row control contacts
42 of the emitter chip 18, and a plurality of column control pads
48, e.g., arranged in a line substantially perpendicular to the
line of row control pads, corresponding to the column control
contacts 44 of the emitter chip. Reverting to FIGS. 2A and 2B, each
of the control pads 46, 48 are electrically connected to the bottom
surface 38 (illustrated in FIG. 4B) of the substrate 32 by a
control via 50 (illustrated in FIGS. 2A and 2B). Each control via
50 extends between the control pads 46, 48 at a top end thereof,
and an emitter drive pad 52, is configured for being connected to a
controller (not illustrated) such as a driving circuit or other
similar device configured to direct operation of the emitter chip
18, at a bottom end thereof.
Reverting to FIGS. 2A and 2B, the row and column control contacts
42, 44 located on the top side of the emitter chip 18 are
connected, respectively, to the row and column control pads 46, 48.
According to one example, as illustrated in FIG. 2A, each contact
42, 44 may electrically connected to its respective control pad 46,
48 via an external conductor 54. The conductors 54 may be wires,
solid leads, or any other suitable connecting element. According to
another example, as illustrated in FIG. 2B, the emitter chip 18 may
be provided with a through-silicon via (TSV) 54 associated with
each of the control contact 42, 44. The TSV's 54 associated with
each of the control contacts 42, 44 are each connected to the
respective control pad 46, 48.
The above examples ensure that the electrical path between the
emitter drive pad 52 and the control contact the 42, 44 are
completely shielded by the overhang 26 of the focus electrode
24.
The focus electrode 24 is configured to correct the trajectory of
electrons emitted from the electron sources 22, while minimizing
loss of electrons emitted at undesirable trajectories. Accordingly,
it is configured to apply a focus voltage across the opening 28
defined thereby, through which electrons emitted by the electron
sources 22 reach the electron receiving construct 14.
Thus, a focus pad 56, configured for being connected to the
controller, is provided on the bottom surface 38 of the substrate
32. A focus via 58 is provided, electrically connecting the focus
electrode 24 with the focus pad 56. The focus electrode 24 is made
of an electrically conductive material, enabling it to apply the
focus voltage at the opening 28.
According to a modification (not illustrated), the bottom surface
60 and opening-facing surface 62 of the focus electrode 24 are in
electrical contact with one another, with at least one or both of
the upwardly-facing surface 64 and a downwardly-facing surface 66
thereof comprising an electrically insulating material.
The electron receiving construct 14 may be provided according to
any suitable design. For example, as illustrated in FIG. 1, it may
comprise a faceplate 68, an anode 70, and a downwardly-facing
radiation source 72, such as a metal target in the case of an x-ray
emitter, or a photoconductor in the case of an image capture
device, as is known in the art.
It will be appreciated that the device 10 described herein with
reference to the accompanying figures may include any suitable
electron receiving construct without departing from the scope of
the presently disclosed subject matter, mutatis mutandis. For
example, as illustrated in FIG. 5A, the device 10 may be a
reflection-type. According to this example, the electron receiving
construct 14 comprises an angled surface 74 facing between the
electron emitting construct 12 and an output aperture 76. When an
electron beam emitted from the electron emitting construct 12
strikes the electron receiving construct 14, radiation of a
predetermined spectrum determined by the makeup of the radiation
source 72, e.g., x-rays, is produced. The disposition of the angled
surface 74 relative to the electron emitting construct 12 and the
output aperture 76 is selected so that the radiation exits via the
output aperture.
According to another example, illustrated in FIG. 5B, the device 10
is a transmission type. According to this example, the electron
receiving construct 14 is disposed substantially perpendicular to
the direction at which the electron emitting construct 12 emits
electrons. According to this example, the radiation source 72 of
the electron receiving construct 14 faces away from the electron
emitting construct 12 When an electron beam emitted from the
electron emitting construct 12 strikes the electron receiving
construct 14, radiation of a predetermined spectrum determined by
the makeup of the radiation source 72, e.g., x-rays, is
produced.
According to the presently disclosed subject matter, the focus
electrode 24 serves as a shield to the control contact 42, 44 and
their respective connections to the emitter drive pads 52. This may
be particularly useful, for example, in high-voltage applications
which utilize the emitter such as an x-ray source, wherein the
burn-in process required prior to its operation (e.g., to create a
vacuum) may result in discharges which may cause damage to the
emitter chip.
Although the foregoing description with reference to the
accompanying drawings was directed toward an electron emitting
construct for an image capture device or an x-ray emitter, one
skilled in the art will immediately recognize its utility for use
in other applications, mutatis mutandis.
The structure defined here in may facilitate the use of cold
cathode technologies, for example for producing x-ray fields.
Those skilled in the art to which presently disclosed subject
matter pertains will readily appreciate that numerous changes,
variations and modifications can be made without departing from the
scope of the present disclosure mutatis mutandis.
Other aspects of the present disclosure relate to an electron
emitting construct operable to emit at least one electron beam
where the electron beam is focused and accelerated by an electrical
field towards a focal spot on an electron anode target. The
electron emitting construct may be configured to avoid ion
bombardment damage to a cold cathode substrate. Accordingly, the
cold cathode may have distinct electron emitting and non-emitting
zones.
The emitter of an x-ray source, such as a cold cathode, is operable
to emit an electron beam toward the electron anode target. The high
current of electrons (30 to 500 mA for medical x-ray) upon
colliding at the target, may cause the target to be heated up to
2,000 degrees in Celsius, accordingly, x-rays are emitted from the
electron anode target. Such an electron anode target may be
fabricated, for example, from tungsten or molybdenum or the
like.
Due to the high temperatures and low pressures involved the
material of the target may be vaporized around the focal spot of
the electrons. Vaporized metal atoms in the path of the electron
beam adjacent to the electron anode target may be readily ionized
by the high energy electrons. The high voltages between the
electron anode target and the cathode which may be of the order to
say 30 kV to 150 kV may give rise to strong electric fields
particularly in the region adjacent to the positively charged
electron anode target where ionization occurs.
Accordingly, metal anions produced in the region adjacent to the
electron anode target may be strongly accelerated away from the
electron anode target along a line perpendicular to the local
electric field, which is typically parallel to the surface of the
electron anode target. The accelerated ions form an ion beam
directed along a trajectory perpendicular to the electric field
adjacent to the electron anode target. When the cold cathode is
disposed along the trajectory, of the ion beam it is vulnerable to
ion bombardment damage.
The current disclosure introduces embodiments of cold cathode x-ray
emitters configured to prevent ions in the high voltage vacuum from
bombarding the cold cathode by deviating the ion beam away from the
vulnerable cold cathode and towards a dedicated and distinct ion
collection zone such that no micro structures are damaged. Such
design may be crucial for application of the cold cathode in
medical x-ray sources.
Various aspects of the current disclosure include segmented
cathodes having distinct emitting and non-emitting zones, angled
electron anode targets, stepped electron anode targets and the like
operable to further direct the ion trajectory away from the
emitting zone of the cold cathode in order to reduce the damage of
ion bombardment. Electron Beam Distribution:
As illustrated schematically in FIG. 6A, showing a possible
technical configuration for a bombardment resistant device 600A,
such as an x-ray emitter, an image capturing device and the
like.
The bombardment resistant device 600A includes an electron emitting
construct 12, including a cold cathode of the emitter, and an
electron receiving construct 14, including an electron anode target
of the emitter. The electron emitting construct 12 comprises a
substrate 32, a cold cathode 22 and a focus structure 42 configured
for emitting an electron beam 80 toward the electron receiving
construct 14, which then produces radiation in a predetermined
spectrum.
The electron emitting construct 12 further comprises an emitter
chip such as illustrated below in FIG. 13A.
The electron receiving construct 14, may be provided according to
any suitable configuration. As illustrated in FIG. 6A, one
embodiment of the electron receiving construct 14 may comprise a
faceplate 68, an anode 70, and a radiation source 72, such as a
metal target in the case of an x-ray emitter, as is known in the
art. The electrons are directed to a focal spot 92 of the
target.
Vaporized metal may be ionized forming an ion beam 90 emanating
from the focal spot and directed away from the target. Ion
bombardment may cause damage even to a conventional metal filament
cathode of a conventional x-ray emitter. It is particularly noted
that cold cathode emitter is particularly vulnerable, and the
bombardment may severely destroy the micro structure of a cold
cathode. To avoid such damage the cold cathode 22 of the
bombardment resistant emitter may comprise an electron emitting
zone and a non-emitter zone, as described hereinafter. The
non-emitter zone 23 may be disposed along a line extending from the
focal spot perpendicular to the surface of the electron anode
target to receive the ionized heavy metal, accelerated by the high
voltage electric field between the anode and the cathode.
Aspects of the current disclosure, applied to the cold cathode as
described hereinafter and to the target anode, will deviate the ion
beam in the high voltage vacuum from the direction of the
vulnerable cold cathode and collide towards a collection zone such
that no micro structures are damaged. Thus, implementation of the
current disclosure may facilitate the application of the cold
cathode in medical x-ray sources.
As illustrated schematically in FIG. 6B, showing a possible
pressure distribution 600B between the electron anode target 70 and
the cold cathode 22 of the device configuration.
The pressure distribution of the device configuration (600A, FIG.
6A) provides low gas pressure in the region 602B in the vicinity of
the cold cathode 22, increasing in the region of 604B and resulting
in higher gas pressure in the region 606B in the vicinity of the
anode 70.
It is noted that some of the gas molecules are ionized by electron
bombardment and the generated ions are accelerated by the electric
field back towards the emitters along a line from the focal
spot.
Emitter Possible Configurations:
As illustrated in FIG. 7, showing a top view and cross section of a
possible cold cathode configuration for an electron emitter 700,
having a centered squared non-emitter zone 706 surrounded by the
emitter zone 704 of an x-ray emitter device.
The electron emitter 700 includes the substrate 702 (sectional
view), the emitter zone 704 and the non-emitter zone 706. The
non-emitter zone 706 is configured to be surrounded by the emitter
zone 704 such that ion bombardment does not occur on the emitter
area 704 therefore preventing bombardment damage thereto.
It is particularly noted that the non-emitter zone 706 material may
be fabricated from or coated by materials that do not contain
oxygen such as pure metal, carbon or various carbon elements such
as a C:H layer, for example.
Further, the size of the non-emitter zone 706 may be larger than
that of electron focal spot. Accordingly, a spreading ion beam
emanating from the focal spot may be collected within the
non-emitter zone 706 without spreading significantly into the
emitting zone 704.
As appropriate the focus structure 42 (FIG. 6A) should be disposed
between the emitter zone and the electron anode target perhaps
surrounding the emitting mechanism. Accordingly, the electron beam
may be focused from the emitting zone towards the focal spot
aligned along a line perpendicular from the target to the
non-emitter zone 702. It will be appreciated that the electrons may
be directed by the focus structure may direct the electrons to
strike the focal spot at an angle to the normal.
It will be appreciated that although the squared sectional view of
the cold cathode substrate is presented by way of example only and
various other configurations may be applicable. Such examples are
detailed further, in the FIGS. 8A-C, as described hereinafter.
Optionally, the emitter zone may be made of additional emitting
elements, to allow the non-emitter zone to be fully enclosed or to
be placed in between emitter zone elements.
As illustrated in FIGS. 8A, 8B and 8C, are schematic drawings of
various cold cathodes configurations of the emitting construct
operable as an x-ray source, according to the presently disclosed
subject matter. The various designs are intended to reduce
substantially the possible ion bombardment damage, generated near
the electron anode target, in an x-ray emitter device such as x-ray
tube, for example.
FIG. 8A illustrates a top view 800A of rectangular configuration of
a cold cathode, having a square emitting zone 802A and a square
non-emitting zone 804A.
FIG. 8B illustrates a top view 800B of rectangular configuration of
a cold cathode, having a rectangular emitting zone 802B and a
square non-emitting zone 804B.
FIG. 8C illustrates a top view 800C of circular configuration of a
cold cathode, having a circular emitting zone 802B and a circular
non-emitting zone 804A.
It is note that the various cold cathode substrate designs, as
described in FIGS. 8A-C, are brought in by way of example.
Additionally or alternatively, various other design may be
applicable providing a shaped emitting zone and a shaped
non-emitting zone, with appropriate zone sizes.
It is further noted that any of the non-emitting zone size, such as
the size of 802A (of FIG. 8A) is larger than that of the electron
focal spot, surrounded by or set between the emitter zones.
Stepped/Angled Anode:
Reference is now made to FIG. 9 showing a second embodiment of a
bombardment resistant device configuration 900 and indicating a
possible electron beam and ion beam simulation. The device
configuration 900 may be applicable for devices such as an x-ray
emitter, an image capturing device and the like.
The device configuration 900 of the second embodiment includes an
electron emitter 902, configured for emitting an electron beam in a
trajectory 908 via a focus structure 906 to an angled target anode
904. It is noted that the angled target anode 904 produces a local
electric field 912 largely parallel to the surface of the angled
target 904. Accordingly, the ions are accelerated along a
trajectory 910 perpendicular to the local electric field and away
from the electron emitter such that the emitter substrate is not
hit, thereby preventing possible ion bombardment damage.
It is noted that a cold cathode electron gun for x-ray source may
comprise a focus structure directing the electron beam toward the
target anode focal spot. The second embodiment of the current
disclosure may include an angled target anode 904 configured such
that ion beam is directed away from the electron emitting
construct. Accordingly, the distance between the target anode and
the cathode, and the target angle, are selected such that the
striking point 911 of the ion beam is lies away from the emitter
zones 902 or the focus structure 906.
In the drawing figures hereafter, various simulations are indicated
illustrating the impact of various angled anode and the relevant
impact of shifting away the ion trajectory.
It is particularly noted that the anode may be configured to be
tilted at an angle to the emitting substrate plane, such that the
emitted electron beam hitting the focal spot on the angled target
anode area with the electrons to striking the focal spot at an
angle to the normal.
As the electrons are accelerated and hit the target anode,
temperature of the focal spot increases substantially (up to 2000
degrees in Celsius) and the anode materials may partially
vaporized. Further, some of the vapor atoms may be ionized by the
electron beam. The ions, which are generated near the target anode
surface have low initial velocity and may be accelerated along a
trajectory perpendicular to the local electric field which is
parallel to the tilted anode plane, such that the ion beam lands
outside of the emitter zone.
It is noted that the position, angle and distance between the
target anode, the cold cathode emitter and the focus structure may
be selected in a manner such that ion bombardment damage is
prevented to the emitter region.
As illustrated in the FIGS. 10A and 10B, the receiving construct
(the electron anode target) comprising an angled anode (404, FIG.
9) may be an angled surface relative to the electron emitting
substrate surface (402, FIG. 9).
FIG. 10A showing a possible design 1000A and illustrates such
angled anode 1002A, where the angle of the surface determines the
ion trajectory 910 (of FIG. 9), which is perpendicular to the local
electric fields adjacent to the surface of the angled target anode
which are largely parallel to the angled surface of the anode.
FIG. 10B showing a possible design 1000B where the angled surface
comprises a stepped angled surface 1002B, configured to have a step
within the surface of the angled anode forming a stepped anode.
It was surprisingly found during simulations that a step along the
angled surface of the anode, even with a small step of 1 mm in
size, makes the electric field near the electron target anode more
asymmetrical causing the ions to be accelerated along a trajectory
having a greater deflection angle such that the ions to be shifted
further outward than those deflected by an angled anode with no
step.
It will be appreciated that although a straight sided stepped
surface is represented in FIG. 10B for illustrative purposes only.
Other embodiments (NOT SHOWN) may have straight or curved steps as
required. Such steps include, but are not limited to, steps having
concave surface sections, convex surface sections, undulating
surface section, saw-tooth surface sections or the like as well as
combinations thereof as suit requirements.
It is further noted that the step location may have greater effect
on deviating the ion beam, if located close to the target anode
focal spot.
Accordingly, an x-ray emitter device configured with a stepped
anode, may have the characteristics such as: The anode may be
configured with at least one step, The step may be located close to
the electron anode target focal spot towards which the electron
beam is directed by the focus structure, The non-emitter zone or
focus structure is fabricated from or coated with pure metal which
may be the same material as the anode material like Mo or W, The
non-emitter zone or focus structure is fabricated from or coated
with carbon materials such as carbon, carbon nanotube (CNT), or
diamond-like carbon (DLC) coating.
Beam Landing Simulation:
Reference is now made to FIG. 11, showing a beam landing simulation
1100 configuration. The beam landing simulation is carried for a
device having an emitting construct comprising a cold cathode 1102
with a focus gate of 3 mm forming an electron beam 1110 directed
toward a target anode 1104 at a distance of 20 mm.
Referring now to FIG. 12A showing an emitter embodiment 1200A
having an emitter chip 1212 is illustrated mounted upon a substrate
1210. The emitter chip 1212 includes nine distinct zones E11, E12,
E13, E21, E22, E23, E31, E32, E33 arranged in a three by three
array. These zones may correspond to row and column control
contacts (not shown) of the emitter chip 1214, The chip-mounting
surface of the emitter chip 1212 may have dimensions of 3 mm by 3
mm. It is noted the emitter chip include an electron emitting zone
and a distinct non-emitting ion bombardment zone. The emitting
zone, for example may comprise the 8 perimeter zones E11, E12, E13,
E21, E23, E31, E32, E33 whereas the central zone E22 may be a
dedicated non-emitting ion bombardment zone.
As illustrated in FIG. 12B, the graph of the beam landing profile
1200B from a 3 mm by 3 mm emitting area, is represented by two
plots: the beam landing width 1230 plotted in micrometer units
(vertical axis 1222) and the beam area compaction 1240 measured in
percentage (vertical axis 1224) and plotted against a horizontal
axis of focus voltage 1220 measured in volts.
Beam Simulation Configuration & Results:
Referring now to FIGS. 13A and 13B, a beam simulation is
illustrated, for various configurations of the electron emitter. In
particular, FIG. 13A, shows a simulation of an angled anode
configured at 16 degrees and FIG. 13B shows a simulation of an
angled anode configured at 7 degrees.
FIG. 13A illustrates a beam simulation configuration 1300A for an
angled anode, resulting in an ion trajectory reducing the effect of
ion bombardment damage. The beam simulation 1300A includes an
emitter 1302A, emitting electron beam 1306A to an angled anode
1304A.
The setup parameters of the beam simulation configuration 1300A,
refer to an anode surface angle of 16 degrees, emitter-anode
distance of 25 mm and emitter-focus distance of 3 mm.
The electron beam 1306A is directed by via a focus structure 1308A
towards a focus spot 1305A on the angled anode 1304A thereby
generating causing an ion beam 1310A along a trajectory
perpendicular to the local electric field adjacent to the angled
anode striking the plane of the emitter at an ion landing area
1314A.
FIG. 13B illustrates another beam simulation configuration 1300B
for an angled anode, resulting in an ion trajectory reducing the
effect of ion bombardment damages. The beam simulation
configuration 1300B includes an emitter 1302B, emitting electron
beam 1306B to an angled anode 1304B.
The configuration parameters of the beam simulation configuration
1300B, refer to an anode surface angle of 7 degrees, emitter--anode
distance of 50 mm and emitter--focus distance of 3 mm.
The electron beam 1306B is directed by via a focus structure 1308B
towards a focus spot 1305B on the angled anode 1304B thereby
generating causing an ion beam 1310A along a trajectory
perpendicular to the local electric field adjacent to the angled
anode striking the plane of the emitter at an ion landing area
1314B.
It is noted that each configuration of anode surface angle relative
to the cathode surface and distance from the cathode to the anode
produces a characteristic ion landing spot as described in the
figures hereinafter. It is a feature of this embodiment of the
current disclosure that the parameters of the configuration are
selected such that the ion landing area 1314A, 1314B lies outside
the electron emitting zone.
As illustrated in FIG. 14A, a result summary 1400A is provided for
the beam simulation of an angled target anode. The result summary
1400A covers ion landing simulation configurations for various
angled target anode surfaces from 0 degrees to 20 degrees, in steps
of 5 degrees, and at distance of 30 mm between anode and cathode,
illustrating the ion beam landing away from its cathode center.
Each plot of the summary result set 1400A, presents ion landing
distance results at a specific anode angle 1402. The distance in mm
away from the cold cathode center is indicated on an associated
horizontal distance axis 1416A. The summary result set 1400A
provides an emitter area indication 1410A, a focus opening
indication 1412A and ion landing area indication 1414A, where each
indication is measured in millimeter distance from the center of
the emitter area 1410A.
It has been found that the larger the angle of the anode to the
plane of the cathode, the farther ion beam landing area from the
cold cathode center.
It is noted that the summary result set 1400A presented, is plotted
for a fixed distance between the cathode and anode of 30 mm, while
the anode surface angle is set at a different angle for each ion
landing measurement.
As illustrated in FIG. 14B, the ion landing simulation results are
presented for various distance values between the cathode and the
angled anode.
The ion landing simulation results 1400B of FIG. 14B refers to
various anode-cathode distance configurations, using a 1 mm
diameter of electron beam focal spot size. The plot of the ion
landing simulation results 1400B is plotted on a horizontal axis of
anode angle 1410B, measured in degrees vs. an ion landing edge from
the center 1412B, measured in mm.
As illustrated in FIG. 14B, plot A provides the ion landing for an
anode-cathode distance of 10 mm, plot B provides the ion landing
behavior for an anode-cathode distance of 20 mm and plot A provides
the ion landing behavior for a anode-cathode distance of 30 mm.
Referring now to FIGS. 15A and 15B, a surprising result of the
simulation is presented relating to a stepped anode. A
configuration was simulated having a stepped anode with a step
height of 1 mm directional along a z axis, showing that even such a
small step influences the shift of ion trajectory further
outside.
FIGS. 15A and 15B illustrated the ion trajectory difference between
a smooth angled target anode and a stepped angled target anode.
FIG. 15A represents an x-ray emitter device 1500A with an electron
angled anode of the electron receiving construct (the electron
anode target). The emitter device 1500A includes an emitter 1502A
emitting an electron beam 1506A to an angled anode 1504A via a
focus structure 1508A, driving the accelerated ions along a
trajectory perpendicular to the electric field, adjacent to the
surface of the anode.
FIG. 15B represents another aspect of the invention, using a
stepped anode, allowing an additional improved design option
compared to the angled anode as illustrated in FIG. 15A.
FIG. 15B represents an x-ray emitter device 1500B with a stepped
anode of the electron receiving construct. The emitter device 1500B
includes an emitter 1502B emitting an electron beam 1506B to a
stepped anode 1504B via a focus structure 1508B, driving the
accelerated ions along a trajectory perpendicular to the electric
field, which is parallel to the surface of the anode. Yet, as
illustrated, the stepped anode is capable of driving the
accelerated ion along a trajectory 1510B, which is further away
compared to the trajectory 1510A, as indicated in FIG. 10A. Thus,
further reduces the possible damage due to the ion bombardment.
It is noted that the step introduced into the angled target anode,
making a stepped target anode, makes the electric field near the
anode 1504B (FIG. 15B) more asymmetrical, forcing the ions
trajectory to shift outward.
It is further surprisingly noted that the location of the step
along the anode surface may be configured to be outside and close
to the electron beam focal spot FS so as to obtain a large
deflection of the ion beam trajectory.
Referring now to FIGS. 16A and 16B, the ion landing spot trajectory
shift away is provided for an angled anode compared to a stepped
anode. The configuration parameters for this simulation include an
anode-cathode distance of 10 mm, an angled anode at 10 degrees and
applied anode voltage of 30 kV.
FIG. 16A represents the simulation results of ion landing spot
1600A using a smooth angled anode of an x-ray emitter device 1500A
(of FIG. 15A). The ion landing spot results 1600A indicates the
emitter area 1603A, the focus opening 1602, and the position of the
ion landing area 1603A, which is towards the edge of the emitter
area 1601.
FIG. 16B represents simulation results of ion landing spot 1600B
using a stepped anode of an x-ray emitter device 1000B (of FIG.
15B). It is particularly noted that the ion landing spot results
1600B indicate the position of the ion landing area 1603B, which is
further away than the hit location 1603A of FIG. 16A.
As illustrated in FIG. 17, the ion landing shift with and without a
step is indicated on a graph 1700. The data of graph 1700 is
presented in a data line 1730, as distance in millimeters of the
ion landing edge from center (vertical axis 1720) for each anode
angle in degrees (axis of anode angle 1710).
Thus, the point location 1732, for example indicates an angled
anode at 10 degrees resulting in a point location of 1 mm away from
the center of the emitter area, while point location 1734, and
indicates an offset of 3 mm away from the center of the emitter
area using a step in the anode of 1 mm in size.
Technical and scientific terms used herein should have the same
meaning as commonly understood by one of ordinary skill in the art
to which the disclosure pertains. Nevertheless, it is expected that
during the life of a patent maturing from this application many
relevant systems and methods will be developed. Accordingly, the
scope of the terms such as computing unit, network, display,
memory, server and the like are intended to include all such new
technologies a priori.
The terms "comprises", "comprising", "includes", "including",
"having" and their conjugates mean "including but not limited to"
and indicate that the components listed are included, but not
generally to the exclusion of other components. Such terms
encompass the terms "consisting of" and "consisting essentially
of".
The phrase "consisting essentially of" means that the composition
or method may include additional ingredients and/or steps, but only
if the additional ingredients and/or steps do not materially alter
the basic and novel characteristics of the composition or
method.
As used herein, the singular form "a", "an" and "the" may include
plural references unless the context clearly dictates otherwise.
For example, the term "a compound" or "at least one compound" may
include a plurality of compounds, including mixtures thereof.
The word "exemplary" is used herein to mean "serving as an example,
instance or illustration". Any embodiment described as "exemplary"
is not necessarily to be construed as preferred or advantageous
over other embodiments or to exclude the incorporation of features
from other embodiments.
The word "optionally" is used herein to mean "is provided in some
embodiments and not provided in other embodiments". Any particular
embodiment of the disclosure may include a plurality of "optional"
features unless such features conflict.
It is appreciated that certain features of the disclosure, which
are, for clarity, described in the context of separate embodiments,
may also be provided in combination in a single embodiment.
Conversely, various features of the disclosure, which are, for
brevity, described in the context of a single embodiment, may also
be provided separately or in any suitable sub-combination or as
suitable in any other described embodiment of the disclosure.
Certain features described in the context of various embodiments
are not to be considered essential features of those embodiments,
unless the embodiment is inoperative without those elements.
Although the disclosure has been described in conjunction with
specific examples thereof, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in
the art. Accordingly, it is intended to embrace all such
alternatives, modifications and variations that fall within the
spirit and broad scope of the disclosure.
All publications, patents and patent applications mentioned in this
specification are herein incorporated in their entirety by
reference into the specification, to the same extent as if each
individual publication, patent or patent application was
specifically and individually indicated to be incorporated herein
by reference. In addition, citation or identification of any
reference in this application shall not be construed as an
admission that such reference is available as prior art to the
present disclosure. To the extent that section headings are used,
they should not be construed as necessarily limiting.
* * * * *